Choosing computer components - memory

My old...ancient Asus M2NPV-VM motherboard with its AMD Athelon64 X2 processor has finally given up the ghost after probably 7 years of use. My case is still good, power supply was tested a few days ago, I upgraded to SATA hardware a few years ago, so now I want to build something new, recycling as much as I can. Update budget is $300 USD

I'm looking at:
MSI FM2-A77MA-E35 - it will fit my existing Micro ATX case
AMD A-10-5800K processor - 6 cores at a great price
Memory - Here I'm stumped. I originally thought to fill it up with 16GB of PNY XLR8 DDR3 1600 memory, but wonder if I'm not better off getting 8GB of something faster. When I look at the fastest DDR3 memory, I notice that CAS jumps from the 7-9 range up to 11 and 12, am I misunderstanding, isn't lower better?

I am not doing hardcore gaming, some stuff in Sketchup, probably the most demanding task I'll do is wanting to devote 4 or 5 of those processors to running Boinc datasets 100% of the time. This is probably what most of the processor time for the last 7 years has been devoted to. I'm looking for longevity, another system that I will be content with for 5 years.

Next upgrade with be a SSD and possibly a dedicated video card, again tailored towards maximizing Boinc datasets.